Electra attestation changes rm decode impl (#5856)

* Remove Crappy Decode impl for Attestation

* Remove Inefficient Attestation Decode impl

* Implement Schema Upgrade / Downgrade

* Update beacon_node/beacon_chain/src/schema_change/migration_schema_v20.rs

Co-authored-by: Michael Sproul <micsproul@gmail.com>

---------

Co-authored-by: Michael Sproul <micsproul@gmail.com>

consensus/state_processing/src/verify_operation.rs

@@ -12,7 +12,9 @@ use smallvec::{smallvec, SmallVec};
 use ssz::{Decode, Encode};
 use ssz_derive::{Decode, Encode};
 use std::marker::PhantomData;
-use types::{AttesterSlashing, AttesterSlashingOnDisk, AttesterSlashingRefOnDisk};
+use types::{
+    AttesterSlashing, AttesterSlashingBase, AttesterSlashingOnDisk, AttesterSlashingRefOnDisk,
+};
 use types::{
     BeaconState, ChainSpec, Epoch, EthSpec, Fork, ForkVersion, ProposerSlashing,
     SignedBlsToExecutionChange, SignedVoluntaryExit,
@@ -366,6 +368,49 @@ impl<E: EthSpec> TransformPersist for AttesterSlashing<E> {
     }
 }
 
+// TODO: Remove this once we no longer support DB schema version 17
+impl<E: EthSpec> TransformPersist for types::AttesterSlashingBase<E> {
+    type Persistable = Self;
+    type PersistableRef<'a> = &'a Self;
+
+    fn as_persistable_ref(&self) -> Self::PersistableRef<'_> {
+        self
+    }
+
+    fn from_persistable(persistable: Self::Persistable) -> Self {
+        persistable
+    }
+}
+// TODO: Remove this once we no longer support DB schema version 17
+impl<E: EthSpec> From<SigVerifiedOp<AttesterSlashingBase<E>, E>>
+    for SigVerifiedOp<AttesterSlashing<E>, E>
+{
+    fn from(base: SigVerifiedOp<AttesterSlashingBase<E>, E>) -> Self {
+        SigVerifiedOp {
+            op: AttesterSlashing::Base(base.op),
+            verified_against: base.verified_against,
+            _phantom: PhantomData,
+        }
+    }
+}
+// TODO: Remove this once we no longer support DB schema version 17
+impl<E: EthSpec> TryFrom<SigVerifiedOp<AttesterSlashing<E>, E>>
+    for SigVerifiedOp<AttesterSlashingBase<E>, E>
+{
+    type Error = String;
+
+    fn try_from(slashing: SigVerifiedOp<AttesterSlashing<E>, E>) -> Result<Self, Self::Error> {
+        match slashing.op {
+            AttesterSlashing::Base(base) => Ok(SigVerifiedOp {
+                op: base,
+                verified_against: slashing.verified_against,
+                _phantom: PhantomData,
+            }),
+            AttesterSlashing::Electra(_) => Err("non-base attester slashing".to_string()),
+        }
+    }
+}
+
 impl TransformPersist for ProposerSlashing {
     type Persistable = Self;
     type PersistableRef<'a> = &'a Self;